There's also this failure case: I know a pair of sisters who look and sound identical enough that they can unlock each other's phones with face and voiceprint recognition.
I knew a girl from Asia that had a sister that was six years younger and twenty pounds skinnier. They could both unlock each other's phones using facial recognition.
Considering the frequency with which facial recognition leads to arrests if you're black [0], it seems that if you've got the right non-white skintone, you can unlock someone else's phone.